Heating furnace



NOV- 27, 1956 L, 1'. PEARsALL 2,772,084

HEATING FURNACE Filed June '7, 1952 .ATToRNEY United States PatentHEATING FURNACE Luther T. Pearsall, Pittsburgh, Pa., assignor to Jones &

Laughlin Steel Corporation, Pittsburgh, Pa., a corporation ofPennsylvania Application June 7, 1952, Serial No. 292,235

4 Claims. (Cl. 263-40) This invention relates to heating furnaces forbillets or similar elongated bodies and is more particularly concernedwith an improved construction of such furnaces to provide more uniformheating of the charge.

Billets or like elongated metal bodies to be rolled are conventionallyheated in enclosed furnaces of the type in which the fuel is burned inthe same chamber with the charge. Such furnaces are commonly built of awidth suicient to accommodate the longest billet to be heated. Thecharging door at the entry end may extend across the end of the furnaceso that successive billets may be introduced broadside onto a pluralityof skids or rails which extend along the furnace hearth from entry endto discharge end. Mechanical apparatus is provided to push the billetscharged along the skids or rails so that when the furnace is completelycharged with a layer of billets side by side the introduction of a coldbillet at the entry end causes the entire charge to move along thefurnace a distance equal to the width of one billet. At the same time, aheated billet is taken out at the discharge end, usually in a directionparallel to the billet axis, and introduced into the mill. It will thusbe seen that conventional billet heating furnaces are relatively longand wide but need not be very high since billets are charged in a singlelayer. only.

lt is common practice to vsupply heat to such furnace at or 'near thedischarge end so that this will be the hottest zone of the furnace. Itis also common to provide a separate zone or subdivision of the furnacechamber at the discharge end, which may be provided with its own heatingmeans, in which the billets soa or remain at rolling temperature aperiod of time sutiicient to equalize their temperatures from center toends. The products of combustion both from the soaking zone and theheating zone are generally led backy over the charged billets to one ormore waste gas olf-takes near thescha'rging end of the furnace. .Thefurnace roof is usually sloped downwardly toward the charging end Vtodirect these gases down onto i the billets and so transferas much heatas possible to the billets entering the furnace. It is diihcult to bringabout a uniform transfer of heat from the waste gases to the incomingbillets in the region near the waste gas oi-takes as conventionallyprovided; consequently, the incoming billets are not heated uniformlyfrom one end to the other.

It is an object, therefore, of my invention to provide a furnaceconstruction which makes possible uniform heating of billets charged bycontrolling the flow of waste gases to the waste gas off-takes. Otherobjects will appear in the course of the following description of myinvention.

Reference is now made to the attached drawing which illustrates anembodiment of my invention presently preferred by me.

Figure 1 is a cross section on a plane perpendicular to the axes of thebillets through a billet heating furnace embodying my invention.

Figure 2 is a` cross sectional elevation through the furnace of Figure ltaken on the plane II-lI.

'Ihe furnace shown is provided with a refractory hearth ICC 2 whichslopes downwardly from entry end 3 to ldischarge end 4. lUpon therefractory hearth 2 are positioned skids or rails 6-6 which extendlengthwise of the furnace. The furnace at its discharge end is providedwith back wall 7 in which are mounted fuel burners 9. 'I'he back wall 7is constructed with a refractory inner lining 10. Adjacent to this backwall 7 is a roof section 12 supported by structural members 13--13 andalso provided with refractory lining 15. This construction forms asoaking zone, previously mentioned, in which the billets remain atrolling temperature for a time prior to withdrawal. The roof section 12adjoins a downwardly inclined section 17 which merges into a verticalcurtain wall 18, also provided With fuel burners 19. Curtain wall 18terminates in a more or less horizontal roof section 20 which issupported by structural members 22-22. The portion of the furnace roofnearer charging end 3 includes a downwardly inclined section 24 whichmerges into an upturned curtain wall 26. This curtain wall 26 forms therear wall of a passageway 28 leading from the furnace roof, the frontwall of which is the curtain wall 30 which merges into a shorthorizontal section 32 extending to the entry end 3. The portion of thefurnace from curtain wall 18 to entry end 3 comprises the heating zonein which the charge is brought up to rolling temperature. My furnace isprovided with vertical side walls 34 and 35. These may be pierced withappropriate cleanout doors 37--37 as required. Side wall 35 is alsoprovided with a discharge door not shown near back wall 7 through whichheated billets are removed in a plane perpendicular to that of Figure l.

The lower edge of curtain wall 26 together with the hearth and furnaceside walls dene the minimum vertical cross section or choke 29 of thefurnace chamber, which I prefer to make approximately equal to theminimum horizontal cross sectional area of passageway 28, previouslymentioned.

Near its entry end my furnace is provided with a waste gas off-takechamber 39 communicating with passageway 28. This chamber may beconstructed with vertical end walls 40 and 42 and an arched roof 41which preferably merges smoothly into the upper edges of curtain walls26 and 30, previously mentioned. A ue 43 leads olf from end wall 42 ofthis waste gas chamber.

Fuel burners 9 are spaced across the width of the furnace and aresupplied with air through air lines 45 extending from manifold 46 whichis connected with air supply line 47. Fuel burners 19 are likewisespacedacross the width of the furnace and are supplied with air throughair lines 50 leading olf from manifold 51 connected to air supply line52. Air supply lines 47 and 52 are both supplied from air line 54, whichmay be supported above the furnace by structural members 56 and 57. Fuelburne'rs9 vare supplied with fuel at junctions 60 by a fuel line notshown, and fuel burners 19 are supplied with fuel at junctions 61 alsoby a fuel line not shown. Fuel burners 9 are positioned to direct flamesmore or less horizontally over the work, whereas fuel burners 19 arepositioned to direct flames downwardly onto the charged billets.

In operation, my furnace is charged at charging end 3 with a successionof billets positioned side by side in the manner previously described.As successive billets are charged, those within the furnace are pusheddownwardly by apparatus not shown along skids or rails 6 until theentire furnace hearth is covered by a single layer of billets. Becauseof the furnace construction and the arrangement of the fuel burners atthe discharge end, this latter end or soaking zone of the furnace ismaintained at a rolling temperature, whereas the furnace temperature insuccessive zones back toward the charging end is successively lower. Thewaste gases arising from the combustion of fuel in my furnace aredirected back over the charged billets toward the entry end of theVfurnace. These gases, of course, tend to rise but are deflecteddownwardly toward the work by inclined roof portion 24. The waste gaseslleave the furnace chamber through passageway 28in theY furnace. roofand rise into waste gas chamber 39 from which they escape into ue .43.

The volume of waste gas chamber 39 is .large relative to that portion ofthe heating furnace directly below it so that the gas pressure inchamber 39 is appreciably lower than in the furnace below and issubstantially uniform throughout.V These .conditions bring about arapid` drop in velocity of the waste gases as they enter chamber 39.Furthermore, the arched roof and smoothly contoured side walls causey noabrupt changes in the ow of gases entering this chamber andkso minimizeturbulence in this ow. Because of this, these gases have no appreciabletendency to channel toward the v side Where the ue is located. The wastegases from the heating chamber of the furnace flow down over the chargeat the choke 29 and upwardly into off-take chamber 39 in an evenlydi'stributed layer or blanket and so transfer heat to the chargeuniformly across that portion of the furnace bounded at one end by thewidth of passageway 28. The area of the charge to which heat istransferred from these waste gases is controlled by the width ofpassageway 28 relative to the furnace heating chamber as will beexplained in the following paragraph and not by the relative location ofthe flue 43. In fact, one signicant advantage of my invention is thatthe flue 43 may be connected to chamber 39 at any convenient pointwithout disturbing the waste gas distribution in the furnace itself.Thus, although I have shown ue 43 Vas entering chamber 39 through oneend thereof, it may enter through the front or back side wall or theroof as is dictated by constructional requirements. y

I have shown waste gas chamber 39 as extending across less than the fullwidth of the furnace, and passageway 28V extending the full width ofchamber '39. It is not necessary that this latter condition obtain, butit simplifies construction to observe it. It is desirable that the widthof the passageway 28 be less than the width of the furnace where thelength of the heating zone, of the furnace is significantly greater thanits width. In such a furnace the heat radiated from the side walls andthe portions of the roof immediately adjacent, such as 32-32 in Figure2, usually raises the ends of billets as they travelalong the hearth totemperatures above those of their central portions. I counteract thiseffect by narrowing passageway 28 somewhat, so drawing the waste gasesawayfrom these hotter ends and toward the center area in order that theheat transferred from these gases to the charge by convection will tend.to equalize the temperature along the billets. The relation between thewidth of the passageway opening into the waste gas chamber and the widthof the furnace depends on the relation between the length and width ofthe heating zone of the furnace. I have found that the optimum width ofthis passageway may be determined to a first approximation from thesimple' relation W2 v X L where X is the width of the passageway, W isythe width of the furnace, and L is the length of the heating zone ofthe furnace. In the furnace shown in the drawings, L from curtainwal1118 to charge end 3 is 45 feet, W is 30 feet, and X is 20 feet,which satisfies the above relation.

While I have shown and described what I consider to be a preferredembodiment of my invention, it will be understood that variousmodifications and rearrangements may be made therein without departingfrom the spirit and scope of my invention.

I claim: f

1. A heating furnace for billets or the like comprising a hearth, sidewalls and end walls, one end wall being provided with a chargingopening, and the other end wall being provided with fuel burnerspositioned to direct heating flames toward the charging opening, a roofinclined downwardly toward Vthe charging opening, .an elongated ywastegas off-take chamber extending ktransversely across the furnace abovethe roof thereof adjacent the charging opening, communicating with thefurnace through a transversely elongated opening, said chamber havingparallel end walls, an arched roof with a span materially greater thanvthe width of the transversely elongated opening, and side wallsconverging smoothly from the base of said arched roof to thetransversely elongated opening, enclosing thereby a volume materiallygreater than that of the portion of the furnace directly below thetransversely elongated opening, and a flue communicating with the wastegas off-take chamber through a wall thereof.

2. The furnace of claim l in which the downwardly inclined roof forms achoke adjacent the charging opening and the transversely elongatedopening directly adjons the choke toward the charging opening.

3. The furnace of claim 1 in which the downwardly inclined roof forms achoke adjacent the charging opening f and the transversely elongatedopening directly adjoins the choke toward the charging opening and vhasa cross sectional area substantially equal to that of the choke.

4. The furnace of claim l in which the transverse dimension of theYtransversely elongated opening is approximately equalto the square ofthe furnace Width divided by the furnace length.

Referencescifed in the me 'of this patent UNITED STATES PATENTS 65,630Bagnall June 11, 1867 .511,800 yRice Jan. 2, 18,94 1,021,144 Gordon etal. Mar. 26, 1912 2,354,324 `Longenecker -Iuly 25, 1944 2,638,334

Jones May 12, 1953

